1. Field of the Invention
This invention relates to a cutting element having at least five cutting edges. The cutting edges are comprised of polycrystalline diamond or the like attached to cemented carbide or a similar hard material which is held by a rotating shaft. The cutting element is so shaped and positioned that it may be used to drill holes.
Throughout the following disclosure, the phrase "polycrystalline material" or "polycrystalline diamond" is intended to cover all super abrasion-resistant polycrystalline materials comprised of randomly oriented crystals which are directly bonded to adjacent crystals, including but not limited to polycrystalline diamond, polycrystalline cubic boron nitride, polycrystalline wurtzite boron nitride, and combinations thereof.
2. Prior Art
Drills used in machining operations usually operate with a simultaneous cutting and wedging action. One common form of these drills is the flat drill. This drill is comprised of a substantially flat portion or blade member and a rotatable shaft. The rotatable shaft has a central axis and its top end may have several configurations. In its simplest form, the top is planar and perpendicular to the central axis of the rotatable shaft while in a version having better support for the flat portion, the top has four surfaces sloping up from the perimeter of the shaft towards the central axis. Also located at the top of the shaft is a slit which forms a diameter line on the top of the shaft running through the central axis of the shaft and from one point on the perimeter of the shaft to another point on the perimeter of the shaft. This slit is positioned so that the four sloping surfaces are divided into two pairs of surfaces.
The slit through the top of the rotatable shaft is adapted to receive the substantially flat portion and hold it in a fixed position for the drilling operation. The substantially flat portion has two opposing pentagonal faces. At the top of the substantially flat portion is a chisel edge which is perpendicular to the central axis of the rotatable shaft. The midpoint of the chisel edge intersects the central axis of the shaft. A vertical plane passing through the chisel edge intersects the vertical planes passing through the lines where the pairs of sloped surfaces meet, usually at a non-perpendicular angle. The top end of the flat portion also has two other cutting edges known as the lips of the drill which extend from each end of the chisel edge and slope downward and away from the central portion of the rotatable shaft.
Each lip provides the leading edge to a cutting lip surface which slopes down from the lip and across the top of the substantially flat portion. The pairs of sloping surfaces of the rotatable shaft are positioned below the top of the substantially flat edge portion, thus exposing part of the pentagonal faces of the substantially flat portion. The cutting lip surfaces terminate at the chisel edge.
The flat portion has two additional cutting edges, called the margins which form the leading edges of margin surfaces at the sides of the substantially flat portion. Each margin is parallel to the central axis of the rotatable shaft and extends downward from the lip along an edge of the pentagonal face. The length of the margin can be varied. A plane containing a margin and the central axis is non-perpendicular to a plane passing through the margin surface. The margin and lip meet at the peripheral corner of the flat portion. These margin surfaces are parallel to each other.
Thus the flat portion has five cutting edges, the chisel edge, two margins and two lips. Each pentagonal face of the flat portion has a margin and a lip and the central end points of the lips provide opposite end points of the chisel cutting edge.
As the drill rotates about its axis, it is forced against a workpiece. As the drill contacts and begins to penetrate the workpiece, the chisel edge is subjected to compressive forces. This results in a wedging or chiseling action whereby the workpiece material displaced by the drilling action moves toward the outer ends of the lips. As this occurs, the lips begin to cut into the workpiece and remove chips or fragments of the workpiece. This cutting action subjects the lips to torsional forces. When a drill is new or recently resharpened, the margins perform no or little cutting action. The peripheral corners, however, remove more material than the inner portions of the lips. As a result, after continued use of the flat drill, the peripheral corners become somewhat rounded. After the peripheral corners where the margin meets the lip begin to wear, the margins increase their function as a cutting edge and the ability of the lips to cut is reduced.
As the lips continue to wear, the compressive forces of the drill must be increased to maintain the ability of the drill to penetrate the workpiece. With workpieces where the drill passes through and out the back side of the workpiece, the dulling of the drill causes burrs or frays at the exit hole of the workpiece as well as requiring increased drilling forces. In blind drilling, where the drill does not pass through the entire workpiece, the dulling of the drill requires additional drilling forces. When the additional drilling forces required reach a predetermined level or where exit holes on workpieces become frayed, it becomes necessary to terminate drilling operations and replace or resharpen the flat drill. The flat drill is usually resharpened by machining the cutting lip planes of the substantially flat portion until the rounded peripheral corners are eliminated. When the cutting lip planes have been machined down to the point where the margins are too short, the drill is no longer an effective cutting element and is disposed. The need to frequently remove the flat drills to replace or resharpen them increases down time in manufacturing operations. Furthermore, drilling with dulled cutting surfaces increases the risk of ruining a workpiece, thereby increasing the amount of scrap created in the manufacturing operation. Both the frequent resharpening and the high percentage of scrap due to dull cutting edges increases the cost of the manufacturing or drilling operations.
Drill bits have traditionally been made from steel. Alternatively cemented tungsten carbide has been used when the drilling material is harder or more abrasive than that which steel is capable of drilling. In cases such as the machining of silicon-aluminum alloys and other materials, even drills with cemented tungsten carbide experience rapid wear at their cutting edges and require frequent replacement.
Recently, the machining of both harder materials as well as more abrasive materials has increased which has introduced a great need for drills which can withstand machining such materials. The use of cutting tools made from wear resistant materials such as polycrystalline diamond or polycrystalline cubic coron nitride to machine harder or abrasive surfaces has been disclosed. (See U.S. Pat. No. 3,745,623 for Diamond Tools for Machining issued to Robert H. Wentorf, Jr. on Dec. 27, 1971). In addition, boring bars tipped with polycrystalline diamond can be used as effective devices for machining the interior surfaces of pre-existing holes. However, none of these tools are designed for or are suitable for drilling new holes in abrasive materials.
In addition to the above tools tipped with polycrystalline diamond, non-planar diamond surfaces with an underlying carbide substrate which provides a backing for the diamond layer have been disclosed. (See U.S. Pat. No. 4,109,737 for Rotary Drill Bit issued to Harold Bovenkerk on Aug. 29, 1978 and U.S. Pat. No. 4,333,540 for Cutter Element and Cutter for Rock Drilling issued to William Daniels and John Cheatham on June 8, 1982). These diamond surfaces are in the shape of a dome or wedge and are used for elements in rock drills where they encounter forces that are substantially normal or perpendicular to the diamond-carbide interface. In each of these prior art devices the polycrystalline diamond surface is supported by the carbide structure against forces applied against the polycrystalline diamond. This diamond-carbide interface is not subjected to torsional forces and consequently is not designed to withstand such forces created during drilling. As a result, these prior art devices use polycrystalline diamond surfaces which are supported in the direction of the forces to which they are subjected and do not employ polycrystalline diamond surfaces which are unsupported in the direction of torsional forces.
3. Objects of the Invention
It is therefore the general object of the present invention to alleviate the aforementioned problems. It is another general object to provide a rotary member employing polycrystalline material on the cutting edges for drilling new holes in abrasive materials where the polycrystalline material is unsupported in the direction of torsional drilling forces. It is yet another general object of this invention to provide a rotary member for drilling holes with cutting edges of polycrystalline material that will wear less rapidly than drills presently available. It is yet another general object of the present invention to provide a blade member or rotary member for drilling holes wherein the polycrystalline material forming cutting edges can withstand the torsional forces encountered during drilling so that they will not chip or break off.
It is a specific object of the present invention to provide a rotary member employing abrasion resistant material for drilling holes in abrasive materials wherein the cutting edges are comprised of polycrystalline diamond mounted upon a cemented carbide surface in planes non-parallel to the axis of the drill such that the diamond is unsupported against torsional drilling forces. It is another specific object of the present invention to provide a rotary member for drilling holes wherein polycrystalline material is deposited on two sloped planes at the top of a carbide substrate such that the leading edges of the resulting cutting lip planes are parallel to the diamond-carbide interface and the polycrystalline material is unsupported against torsional drilling forces.